text:
How many four-engine commercial passenger jetliner types are currently in use?
Just heard following somewhere:

It is easy to distinguish four-engine passenger jetliner type, because there are only three of them:

if it has "hump" upper deck then it is Boeing 747,
if it has two decks then it is Airbus A380,
otherwise it is Airbus A340.

Is this statement true?
I'm asking about commercial passenger jetliners only. So no cargo, no military etc.

Please clarify (by editing your post) what is the focus of the question: How many 4-engine airliners in the world? (title) or how to identify them? (body). I assume this is the latest, but without clarification, you may get answers to the title question.

Wonder if I'm the only person surprised there's so few aircraft in this list - I would have thought there were way more than a couple of single-deck four-engine airliners in common use.

@mins "How many... jetliner types", so I assume this is quite straightforward, right?

"It is easy to distinguish four-engine passenger jetliner type... Is this statement true?" is also quite straightforward, but not the same question. So do you want to know about the number or whether they can be distinguished easily (and optionally how)? Fortunately enough the selected answer cover both questions.

There's at least one more that's in use (albeit not very common use), the Ilyushin Il-96, but that one's very visually distinctive anyways.

@Vikki-formerlySean The Il-96 is already mentioned in the answer below.

Well, the 3 points you make are easily demonstrable to be true, and also a fairly unique feature of all three if looked at side-by-side.
The 747 is the only one with an obvious hump towards the front of the aircraft. This upper row of windows is unlike either of the other two

Photo Aldo Bidini:: source: http://www.airliners.net/photo/Alitalia/Boeing-747-243B/1200648/L?sid=f499b3169d12a0d4f410846e6512443a
The A380 has an entire upper row of windows - it does indeed have 2 full decks.

   Richard Vandervord source: http://www.airliners.net/photo/Etihad-Airways/Airbus-A380-861/2574151/L
If it has 4 engines, but neither a half upper deck and hump or a full upper deck (and it's an airbus!) then yes it is an A340

Aero Icarus source: https://www.flickr.com/photos/46423105@N03/5445375360/
However, that is not all the 4 engine passenger aircraft.
The BAe 146 is a 4 engine regional airliner, and you could add to your distinguishing features "has a T-tail, must be a 146". It is also the only one of the bunch with a high wing.

   Adrian Pingstone source: https://commons.wikimedia.org/wiki/File:Lufthansa.rj85.arp.jpg
And then we're into the Ilyushins. The Il-96, is easily distinguishable from the similar(ish) A340 as it is considerably smaller - hard to tell from a close-in photo, but in real life if one were parked next to the other the IL-96 is smaller.

Anna Zvereva source:https://www.flickr.com/photos/130961247@N06/31268448486/
The Il-86 has 4 engines but does not fit your criteria, as it only remains in service with the Russian Military, but the Il-62 is still in commercial service. It's very easy to distinguish by having its 4 engines mounted on the tail

Tim Rees source: http://www.airliners.net/photo/LOT---Polish/Ilyushin-Il-62M/1033235/L

The Ilyushin Il-96 is still in use.

The II-96 is easy to distinguish - it is so small, the size of an A320 or B737, yet with 4 engines.

@mins yes I guess so. Its just looking at pictures the scale is a bit hard to distinguish. If there was an A340 parked next to it I think it would be very obvious!

The Il-96 is more the size of a 767 than a 737 (if not larger). And of course there are still DC-8 and 707 variants in operation as well, maybe some Il-86 variants too.

@jwenting DC8 - 3 still in service, all cargo. No 707's still in airliner service. Travolta still owns one, but I dont think that counts! Il-86 I covered in answer (military only at this time)

@Jamiec: Your edit makes this answer a very good one!

Thanks @mins. I like this sort of question, thy're pretty benign but fun to research :D

For whatever it's worth, the newer aircraft from the BAe 146 family are known as Avro RJs instead.

The high wing of the 146 is a giveaway too.  And the IL-62 also has a T-tail.  Even with the sun behind them you're unlikely to confuse the two because of the different proportions.

@ChrisH Yeah, the high wing and the small size are the biggest giveaways for the 146. I don't think it would be very hard to tell the difference in size between a 146 vs. a 747, A340, or A380...

@reirab no, and when I needed to ID aircraft on approach (90s) they were among the smallest we saw. IL-62s weren't exactly common at LHR or LGW then either.

I'd distinguish the BAe146 by the fact that it's tiny compared to the other planes. But the T-tail and high wing are also valid. :-)

@kevin the Il-96 is more the size of a 767 or A300 than a 737 or A320. It's a wide body airliner.

Are there any Vickers VC-10's still in commercial service?

@NeeravDodhia I highly doubt it. But if you find evidence to the contrary i'll happily add it in.

@Jamiec I'll have a dig when I get home from work

Regarding the Il-62, I'm not sure Air Koryo quite counts as commercial service.

You can add the BAe 146 to the list.

This should be a comment, or build a full answer for: "It is easy to distinguish four-engine passenger jetliner type [...] Is this statement true?"

Boeing has B747 with 4 engines.
Airbus has A380 and A340 with 4 engines.
Antonov has an-124 with 4 engines and an-225 mriya with 6 engines.

While not very clear, the question is about distinguishing features of airliners with four engines. So how do you identify all of them?

@mins the question as written is about whether a statement that there are only 3 types of 4 engine jetliners is true, not how to distinguish them. So an answer stating there is a 4th type answers the question (no, the statement is not correct).

@mins the question text reads "Is this statement true?" so is about the statement, not the differences between other aircraft.

An-124 and An-225 aren't airliners and aren't in passenger service (question excludes cargo and military aircraft.)

As for clarity of my question, I agree. It could be much clearer. I must find some time to edit it to become a bit better. As for reirab's comment, it is true. I was asking about passenger airliners and thus I had both Antonovs in my mind, but that's not what I'm talking about.

Well... we should not forget legacy aircraft still in use. You might also spot some Douglas DC-8 still in use. In this link I have been able to find 8 planes still in use.
This figure via wikipedia:
In order to identify this old model just look to the engines, old fashion slim hets and look to the wing tips, there is no wing tip device.

There's still John's 707 flying around - not commercially granted.
There's the VC-10 that could be confused with the IL-62. Only military now but was commercial.
And the Avro 85/100. Same but different from the BAe 146.
Bit too picky?

John Travolta returned to the Australian Historical Aircraft Restoration society (HARS) museum near Sydney. ref -> https://www.flyingmag.com/john-travolta-donates-his-boeing-707-to-australian-museum

As stated in other answers, there are quite a few more 4 engined jet liners than just the three types stated in your claim.
Identification of the 747 and A380 is pretty simple indeed and correctly asserted in the claim.
Other types will all have their own characteristics, which would have to be found by studying photos and/or drawings of the aircraft in question (and possibly knowledge of which types can be expected at a specific airport, e.g. you're not going to find Il-62s in western Europe because they're banned there for noise abatement reasons).

IIRC, the reason commercial (or "commercial") Il-62 flights are banned in Europe is because they're operated by Air Koryo, rather than for noise reasons (the two remaining Il-62s in scheduled passenger service are both Il-62Ms, whose engines can be hushkitted to modern noise standards).

@Vikki-formerlySean no, the ban on Il-62 flights predates the dissolution of the Warsaw pact. In fact one of the reasons Interflug was looking to buy A310s was the impending ban on them using their Il-62s on flights between East Berlin and places like Amsterdam (they operated Amsterdam-East Berlin-Leningrad at the time using the type).


text:
Since when black box is called "black box"?
In addition to this question. Is there any noted moment of time when "black box" name was first time used for calling actually orange-painted FDRs? Was there any other name ("orange box"?) before?
Or is it that they have been called "black boxes" ever since actual introduction to aircrafts?

I'm voting to close this question as off-topic because maybe it belongs to http://history.stackexchange.com

Voting to reopen. Certain users here seems to be missing "since when" part or seems to be getting it equal to "why", which is an obvious mistake. I want to know since when black boxes are called black boxes (i.e. is there any recorded moment in aviation history when black boxes were not called black boxes?)? Such information is not provided in linked question and thus marking this question as duplicate is a misunderstanding as per me.

There are answers to the linked question that do address the "since when" part as well.

@fooot Judgement depends on how you understand "exact duplicate" meaning. My question, by no mean, is an exact duplicate. Following your way of thinking, asking question "Which newspaper or dictionary first time noted usage of 'black box' meaning" would also count as an exact duplicate of that question. I think, you see my point. There are literary dozens of things addressed "as well" in linked question. But, that is not the way how we should understand "an exact duplicate" meaning here, right?

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
How fast can an F-22 scramble?
The startup process in many military aircraft is, complicated, to say the least.
It takes a lot longer than most would think. An F-16 from cold is required to be able to scramble within 5 minutes if on alert (armed, fueled, and pilot ready), 15 minutes if not.
I also know that during the Cold War when the situation was expected to deteriorate, they could deploy B-52's to all runways (civilian airports included) that were longer than 9,000 feet, just sitting there with engines running ready to go. (Terrifying to think about...)
I also found this:

Default NATO QRA alert time is 15 minutes (in DEFCON 5), although the local CRC can lower that to ten (DEFCON 4), five (DEFCON 3) or even two minutes (DEFCON 2) depending on current state of affairs.
At 5 minutes (DEFCON 3), the engines would be running idle 24/7, at 2 minutes (DEFCON 2) there are pilots in the cockpit 24/7.

Anyways, an F-16 can scramble in 5 minutes. But an F-22 has an automated start process. IIRC, the checklist is something like...

Master Switch On.
Throttles Forward to idle.

I understand that this may be classified, but I was wondering if anyone can put me in the ballpark.

Why would that affect scramble time? Is the startup time mostly determined by how long it takes a human to flip switches, or by how long it actually takes things to happen (especially at that speed)?

@cpast One would assume that if the pilot's attention could be diverted elsewhere during an automated startup, that the entire process would be faster, and more could be  simultaneously accomplished.

The actual startup of the engine doesn't take terribly long. And standard practice is to monitor the engine start, so I doubt it can scramble much faster than another fighter (if anything, I suspect an F-16 can scramble slightly faster because it only has 1 engine)

In the military, if its a no-kidding scramble, the normal checklist will not be followed, and you can guarantee that the pilot will be strapping in while the jet starts and getting his aircraft moving as expeditiously as possible.  Furthermore, the F22 automatically performs the BITs and runs through the checklist on its own.

@SHAF There's a description of a scramble here: http://www.historycommons.org/entity.jsp?entity=heather_penney_garcia Penney Garcia, who is a rookie pilot, will later say: “I’d never scrambled before, I’d never done this. I was screaming to the maintainers to pull the chocks, and the guys were pulling the pins to arm the guns. We were going without INS [inertial navigation system].” Sasseville and Penney Garcia are airborne about six minutes after reaching their jets.

@ChrisW Yep, sounds about right.  You can always perform an airborne INS alignment, it just takes longer, and you dont get things like the velocity vector until you're aligned.

@ChrisW Scrambling with only TP rounds doesn't make sense. How long could it possibly take to put a pair of sidewinders on the pylons? Granted, TP rounds could easily take down an airliner, but they weren't sure WHAT they would be dealing with when they got airborne.

@HCBPshenanigans I'm pretty sure they don't just leave Sidewinders around on the tarmac in case someone needs them. And I'm also sure (and hope) that if you ran up to the armoury and shouted "I need two Sidewinders, stat!" they would ask questions rather than just hand them over.

@DJClaywort One day Russia decides to invade. Better do some paperwork to get my missiles... Yeah, okay... If a scramble order has been issued, I guarantee the whole base knows by then. And I would put money on an armament crew being standing by at nearly all times.

@SHAF I'm not so sure. Granted, They aren't going to keep things fully armed all the time, but keeping your required alert fighters with a few sidewinders (Not live at that point by the way! Remember those pesky remove before flight tags?) is just common sense.

@SHAF Now that is a more reasonable answer. (FYI, forrestal incident occured because they pulled the pin too early). I think the most reasonable answer is the elemental exposure.

The planes and pilots had just returned from the "Red Flag" Nevada exercise ... so they were loaded with training ammo, not live missiles. Guards planes in Washington, not NATO QRA. They were installing missiles on two other planes. I think those planes took off 29 minutes later (i.e. at 11:11 instead of at 10:42).

Reminder that comments are not for extended discussions, especially about matters not directly related to the question.

For military aircraft on "alert", there is a position called cocked on (or as some news sites call it, "hot-cocked").  This procedure is run before the aircraft is placed on alert, and does a pre-flight check of all the instruments and then places them in a state that allows power application in a rapid manner.  This way, only minimal steps are required for the aircraft to be ready.  In addition to cocking on the aircraft, they can be parked in special areas (some are called Christmas Trees because of their appearance). This allows the aircraft to reach the runway quickly. Also, in the old SIOP days, there was an Alert Facility near where the aircraft were parked, where the crew would stay in a state of readiness.

Currently the full SIOP mission isn't active (it was ended in 1992 by President Bush, but there are still forces dedicated to it in a new capacity). However, the facilities still exist on many bases.  They can use these facilities still for whatever alerts are required.
With an aircraft in cocked on position, with a pilot on alert (cockpit or facility), an aircraft can take off in a very, very short time (from seconds to minutes).  In general, the mission requirements will dictate the amount of time that the pilot is given to take off (as you note in your question).  So sadly, I can't give a specific answer to your question, because it depends on parameters you haven't specified.

You can start an f-22 in about 2 minutes or less. The procedure is

Master Batt.
APU(Auxiliary Power Unit)
Flip 2 generator switches
flip nav and position lights as required for mission
Make sure fuel switches are set right
Wait a couple seconds for APU to finish start up
push throttles to idle
configure MFDs as needed as engines spin up.
taxi to runway

Welcome to aviation.se. Would you happen to have any source?

Yeah running the flight sim made by IRIS which was done for Prepar3D for Lockheed with their oversight. That is the process I go through to get the jet up and running from a cold dead start. I am sure the pros can do it way faster than me. And I am sure the MFDs are probably set up the way the pilot likes from the get go.

You could setup the lights on the ground roll. or while on climb (if procedures allow). To gain 3-4 more seconds.

That’s not an acceptable or reliable source.

There is no set time because there are too many factors. On a large airfield it could take more than 5 minutes just to taxi to the runway. If you maintain a plane on alert (expensive and time consuming), you could get it rolling inside of 5 minutes. That means:

The pilot is fully ready and has all his stuff ready to go; literally waiting to jump into the plane
The aircraft has been pre-flighted, fueled and is on the apron ready to go
Munitions have been loaded and checked

Needless to say, keeping aircraft in this condition is expensive and I would imagine is only done at certain specific airbases where some special need for a fast launch is required. Loading and unloading weapons is a very time-consuming process and there is a lot of red tape associated with it.
The time constraints have nothing to do with the type of aircraft. It's more a question of the human factor and lots of little things.
Also, another factor is how much you are willing to skip. You might have a 40-point checklist and 25 of them are "optional" items that pertain to safety. If you don't care about dying, feel free to ignore them and you can take off 5 minutes faster.

I think the original question is geared away from aircraft on alert, and specifically more towards aircraft that are scrambled to meet a surprise threat (like on September 11th).  Furthermore, certain aircraft are much easier to start and get airborne, and if its a matter of life and death, nobody is going to follow a complete checklist.

As some other answers have mentioned, and some haven't, it varies very widely by readiness - whether the aircraft was expected to need to scramble.
The usual time for an aircraft to scramble in modern wartime would be 15 to 25 minutes. This is from normally maintained readiness, for a typical post-cold-war conflict. This figure came from a flight line ops Lt.Col (not a pilot, the guy responsible for getting planes ready to fly), unofficial, but it aligns well with other information.
Newer aircraft are not much faster to start, since the steps are the same, and pilots know them; automation just simplifies it. There's still more to it than just one switch. The Chegg answer (hardly a place for such info) that seems to have been quoted in the question is not correct.
Engine ground running can be appropriate when an attack or a major war is expected. Running aircraft can't be refueled, the pilot can't leave the cockpit, and parts run up the hours, so very few planes can be kept in such a condition. Given how few F-22 exist at all, the US could realistically maintain 2-4 flights at such a readiness level.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What factors influence the maximum speed of an airship?
I'm interested in learning about the physics of airships; in particular, how you determine an airships maximum speed.
For example, the Hindenburg topped out at about 80 mph. The ship itself weighed about 130 tons, not including cargo, passengers, etc.
If it weighed less could it have achieved a higher top speed, or would 80 mph have been about the fast it could have gone regardless, for other reasons such as drag/air resistance?
If it had twice as many engines, could it have gone twice as fast?
These are oddly specific, noodly questions, and I'm not looking for the answers themselves, but rather I'd like to be pointed in the direction of the math/physics fundamentals for getting the answers. I'm working on designing some fantasy airships for an RPG, and of course while they're not real and very fantastical, I do want them to have some semblance of verisimilitude, and imposing real world physics (with some wiggle-room for the fantasy part) I think helps a lot.
Thanks so much for your time and answers!

I'll do this without most of the math since your target audience won't want to read equations in your story.
In the simplest terms, the maximum speed of an airship occurs when the maximum thrust generated by its engines is equal to the drag it experiences while being pushed through the air at that speed. That drag depends on the diameter and length of the airship (more specifically, the projected frontal area and the total "wetted area" of the entire vehicle's outer skin).
This is a complicated business because the relationships between all of those variables are strongly nonlinear- for example, the drag varies with the speed squared and the power required at a given speed varies with the cube of the speed.
So in your story: doubling the power of the engines will increase the airship speed only slightly, at the cost of doubling the fuel burn rate and therefore the fuel tank capacity- and thereby reducing the useful payload.
Similarly, doubling the length of the airship will roughly double the wetted-area drag, which means you have to double the horsepower of the engines or their number in order to achieve the same maximum airspeed as the shorter airship.

Thanks for the information! I'm not writing a story, it's a TTRPG like Dungeons & Dragons. Right now it's just drawings and sketches at the moment. Just trying to get realistic specs like size, weight, lift capacity, etc at the moment.

The top speed depends on the type of the airship. While the first designs were non-rigid, it became soon obvious that useable speeds could best be achieved with rigid designs because the higher dynamic pressure at higher speeds required more internal pressure to maintain the hull's shape. Given the low strength of early hull materials, the internal pressure puts a firm limit on non-rigid airship speeds.
Both designs produce drag mostly from friction and here size helps. A larger airship has a higher Reynolds number at the same speed. Its drag, being proportional to the wetted surface, only grows with less than the square of the linear size increase while lifting capacity is proportional to volume or the cube of the linear size. Next, the additional drag of the car, fins, gondolas and their rigging is a substantial factor: In case of LZ 126, S. Hörner (page 14-1) gives the drag coefficient as $c_D = 0.023$ for the hull alone and $c_D = 0.071$ for the complete ship, including nacelles, fins and all. The reference area here is the airship's frontal area.
A similar result is given in NACA Report 394 which documents the tests done on models of Goodyear Zeppelins in the NACA variable density wind tunnel in 1932.
As others have pointed out, speed does not increase in proportion to thrust, but increased thrust will result in an increase a bit larger than the square root of the thrust ratios due to the Reynolds number effect (friction drag changes approximately in proportion to $\text{Re}^{-0.2}$). Depending on the means of propulsion, thrust itself drops with speed for a given power with propeller or bypass engines. Only with rockets will thrust be constant over speed.

Drag coefficient over Reynolds number for an airship hull from NACA Report 397.
In order to calculate the top speed of airships, first wind tunnel tests on models were performed in order to find the drag coefficient of the general shape. Next, that result was scaled up to the real size and then the effects of the car, fins, gondolas, struts and bracing wires were added. The results were calibrated with deceleration tests on real airships. By measuring the change in airspeed of the unpowered airship, the drag over speed can be determined, and those results have been collected in NACA Technical Report 117 by Max Munk (1921) and NACA Report 397.
In order to make existing Zeppelins larger and faster, hull extensions were added together with additional engine gondolas. For your RPG, therefore, you should also have modular designs where the number of engines can be selected. Each one adds some thrust but also increases drag a bit.
Actually, the dynamics of airships are much more interesting than their top speed. In order to pitch up, the horizontal fins need to produce a downforce. If speed is low, this will force the airship down. Increase speed, and there is a point where no altitude gain is possible with elevator deflection. That is called the critical speed. Only when the airship flies faster than its critical speed will control effectiveness be restored. In case of the Cargolifter CL-160, power had to be increased by 40% from the initial design in order to stay well above its critical speed.
Also, maneuvering is an art in itself: If the ship sinks into warmer air, the adiabatic heating of the lifting gas might not be enough to maintain lift and the ship picks up sink speed. Now dynamic lift needs to be added in order to avoid a crash unless plenty of water ballast is available for dropping to lighten the ship. Size is now a disadvantage: Since aerodynamic lift is proportional to the hull area but lifting force proportional to its volume, larger ships can create less aerodynamic lift as a proportion of their static lift. While small ships can easily add or subtract 10% of their lift by means of pitching up or down, the Cargolifter flight envelope allowed only for ±4% of aerodynamic lift.

As for the weight vs. speed: a rigid or semirigid airship has a max takeoff weight, which depends on it's size (because the size pretty much determines the max lift). If this airship was to fly, say, only half of the max weight, it would not go any faster, as the drag would be the same because the size does not change.
An airship may lift a load heavier than the buyoancy it has, by using engine power to create lift. This is by no means good for fuel consumption, but some modern airships have a lifting body shape, so part of the lift is created by the airships forward motion through the air. Such a ship uses steerable engines to produce extra lift on takeoff and landing. This kind of airship is faster than a traditional "blimp" of same weight and power.
Also, it matters what "floats" the airship: helium, hydrogen, or, being a fantasy game, even vacuum maybe? Hydrogen gets you better buoyancy than helium, so an airship filled with hydrogen would be able to lift x tonnes more than the same ship filled with helium, or lift the same weight with a smaller volume of body and therefore be faster with same engine(s). We of course know the downside of hydrogen, it's an accident waiting to happen.
My ad-hoc tongue-in-cheeck proposition of vacuum airship (vacship?) Would be most efficient (per unit of volume), but in a non-fantasy world, next to impossible to construct.
As for the scaling, niels gave you the basic formulas for speed vs. drag vs. power. If you will, dig up some formulas and find relations between volume, diameter, height (or rather length in this case), and skin area of cylinder to roughly optimize the size of an airship.
Some other aspects to consider in the game: Heating the buyoant gas would increase the lift a bit, but again, not a good idea with hydrogen. A hydrogen filled airship could use the hydrogen also as a source of energy for the engines... Being a fantasy game, you of course have the possibility to strech the limits of the real world as you please, just google some historical and contemporary examples and sprinkle them with some magic :)

Vacuum ship would not be more efficient. That's because you can't compare the “lift media” alone. You are creating a construction to displace air, and the lift medium is part of that structure. If the lift medium is a light gas, the enclosure only needs a moderate strength in tension and no strength in compression, because the gas inside keeps in tensed, which can be done with very light fabric. But to enclose vacuum you'd need a lot of compression strength and there are no light materials for that. So the envelope will end up much heavier than gas filling would be, making it less efficient.

@Jan Hudec yep, you seem to have missed the part "... in a non-fantasy world, next to impossible to construct."

I didn't miss it. I am saying that claiming “would be more efficient” is incorrect as far as you must include the weight of the container in the efficiency comparison. Even in a fantasy setting, especially if it is supposed to keep some level of realism.

@JanHudec Ok, so let's say we make the container of adanmantium? Jeez, this is a question about a fantasy game, loosen up a bit! It's not everyday you get to be silly on ASE :)

@Jpe61, thanks so much for your reply! You are correct, I did have in mind a vacuum airship. Although there may be some vessels that utilize hydrogen, the big innovation will be a special metal that keeps its shape after the air has been evacuated from a container made of the material. And to be hones,t it's not for a standalone game, but some ship stats for a Pathfinder game. So a lot of this is fluff/irrelevant anyway, but if I'm going to make up little background details, I want them to at least sound plausible.
Thanks again for your time in crafting your well-thought out response!

@Jpe61 could I run some numbers by you? I think my math checks out but I'm not confident. Suppose I had a container made of a fantastical material that held its shape when the air was pumped out, to allow for the mythical vacuum airship. If this container were a cylinder 20 meters tall and 50 meters long, with spherical ends (basically a pill shape) it would have a volume of 96,341 cubic meters. Air weighs about 1.29 kg per cubic meter, and since it would displace 96,341 cubic meters of air, it should lift 124,279 kg, right? minus the weight of structural elements, air humidity, etc.

https://en.wikipedia.org/wiki/Vacuum_airship#Principle I, too, was interested in vacuum airships, but they are disappointing. Helium has only a 14% lifting penalty compared to vacuum and can eliminate the pressure differential.  Even though hydrogen is only half as dense as helium (basically), it still only gives about a 7% advantage over helium. Not really a game-changer, IMO.

@LawnmowerMan: Indeed. What matters for buoyancy is the difference between the densities of the air outside and the gas inside the balloon. Compared to the nitrogen/oxygen atmosphere on Earth, both hydrogen and helium are very close to weightless. (See also: Why do we use helium in balloons? on [chemistry.se].)

Fair enough, the dirrerence seems miniscule, but as there seems to be a common drive to keep this stuff down to earth (pun intended), remember that aviation is a business where companies eagerly chase savings and improvements of less than a single percent and are happy to gain them...

@Jpe61, but would ultra-thin adamantium foil supported by pressure of hydrogen inside be heavier than a solid adamantium shell holding vacuum? Even with fantasy material it is not clear.

An empty airship has the same inertia as a fully loaded one. The missing payload is replaced by heavier air in its envelope. An airship will always weigh approximately the equivalent of the displaced air.

OMG what a brainfart from me, thanks @PeterKämpf, I stand corrected! In a case of a lifting body airship this would be a bit different, but I guess the difference would be neglible.

Comparison of two giants from the golden age of airships LZ 127 Graf Zeppelin and LZ 129 Hindenburg provides some useful information on your proposed scaling.
Both airships were around 800 feet long and cruised at 80 - 85 mph.  Hindenburg was 35 feet wider, with more than double the lifting capacity, but required 4 x 1200 hp compared with 5 x 550 hp of the Graf Zeppelin.  The increase in girth of the Hindenburg resulted in an 82 % increase in its frontal area, which matches well the increased power required.
Would increasing length and decreasing diameter be a better way to make it faster? Absolutely yes, as racing scull design, Concorde, and this answer imply, with one caveat, many airships that were lost in turbulence, due to their great size, literally put one end in the updraft and the other in the downdraft, resulting in overstressing and failure of structural components.
Putting the Hindenburg engines on the Graf Zeppelin would result in a 40% increase in speed, as WindSoul points out, but again structural stresses would have to be evaluated.
Reducing weight would affect speed only if it results in a more aerodynamic shape that produces less drag, as compared with heavier than air craft that can reduce their wing AOA or speed to lower drag with a lighter load.
So, at the expense of more power, the stockier design would be much safer, and be able to carry more load.  Apparently this is what the designers of Hindenburg had in mind, as well as helium, which they were unable to obtain.
For a modern hybrid approach you may also wish to check out the Hybrid Air Vehicles
Airlander 10 for more ideas.

Note though that by making the airship longer and thinner you are increasing the surface area for the same volume, which increases weight (reducing payload), and part of the drag also depends on wetted (surface) area. So there is optimal fineness ratio.

@Jan Hudec Need to quantify both frontal drag area and wetted area drag effect.  Take a football and an arrow.  But PK pointed out much of the drag was from the gondola and fins, and Reynolds number was important.  This caused me to compare the Graf Zeppelin to another contemporary, the R 101.  The Graf had a shape more like a supercritical airfoil!

Reducing weight reduces the need of lift and therefore makes the airship smaller and reduces drag. Unlike airplanes, mass and volume of airships are closely related.

The drag increases with the square of speed. Since thrust only slightly overcomes drag, doubling the thrust only results in a 40% increase of speed.
In the case of a dirigible, doubling the thrust won’t double the speed. It will only increase the speed by 40%.
There are other factors to account. Once the flow approaches transonic speeds meaning the speed of sound might be reached on locations on the surface of the ship, then the drag increases considerably due to initiation of the shockwaves. At that time the drag formula needs adjusted.
To wrap it up: while subsonic, doubling the thrust only increases the speed by 40% for the same aerodynamic shape. If the increase of thrust reached transonic flow of air around the aerodynamic shape, then the schckwaves will increase the drag considerably and put more stress on the airframe. Increasing the speed beyond supersonic will require the study of how shockwaves develop on the airframe. The pressure increases, the temperature increases as well. At a point in hypersonic flight the shockwave detaches completely from the airframe and forms ahead, leaving the airframe engulfed in a pressurized bubble where the friction of pressurized air flowing on the surface creates heat.

A supersonic airship, now there's an idea... :)

Please do not waste anyone's time with comments leading to nowhere. If you have a need for clarification in terms, like in this instance supersonic or airship, then by all means ask. Thank you.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How in-flight close-ups are captured
What equipment and preparations are necessary to shot a picture like this (an in-flight close-up, clearly shot over a large body of water, possibly from a short distance):

This question is somewhat similar to my question asked at Travel half a year ago. But, in that picture plane was captured during final approach, over a city, supposed from some building (actually turned out to be shot from a helicopter).
I assume that using a telescope or shotting from any building won't help much in shooting such picture as above. If not, then what? A drone? Again, a helicopter?

From the perspective you can see the only possibility is being above the aircraft, not on the ground. I wouldn't be surprised this is a 3D synthetic rendering, as the reflection on the nose is quite unnatural (anisotropic) for paint.

related: https://aviation.stackexchange.com/questions/16487/how-are-aircraft-filmed-in-sky

It could also be a doctored image, with the aircraft photographed and the background added later.

@mins to me is quite a natural image shot with a telephoto lens

@mins and Jamiec: As per my knowledge, the image is as natural as can be and it is neither rendered nor modified in anyway. However, as per Federico cite of related question, my questions seems to be a dupe.

@Federico: I was referring to the dry paint reflection, which is normally more diffuse, but I agree that without a less compressed image, it's difficult to say (neat reflection from 3D rendering)

@mins On the other hand it is hard to not agree with you that this reflection looks a little bit artificial / unnatural.


text:
What is the major source of engine noise for non-propeller aircraft?
Sparked by this question:
Take any non-propeller powered aircraft, when idle, the sound produced by the engines are fairly low pitched, and as the engine spins up, increasing in pitch before becoming a full on roar.
I figured that the major sources of engine noise could be

The air rushing out of the exhaust,
The noise of combustion in the engine,
The mechanical noise of engine parts

My question is what causes the majority of the engine noise at idle vs full power.
To stop this question being too broad, lets discount noise coming from any source that's not the engine's of the aircraft in question. I just want to know about engine noise.
I had a look at this question, but that doesn't have any information about the source of engine noise, just that the turbine itself will also produce noise which is something I didn't consider.

This is just a guess, but its possible that a good portion of the noise is the air being sucked into the nacelle, then on the other side when the compressed air expands through the exhaust could create more noise as well. I'm sure there are noise studies of jet engines somewhere, but I can't find them...

The exhaust makes most of the noise. Engines with higher by-pass ratios generally makes less noise. The shape of the exhaust nozzle also has a great impact. That's why most hush-kits look a bit funny.

Related: Sources of Aviation Noise --- Why are aircraft noisy and what can be done about it? --- Technology for a quieter America with this visual comparison between 60s and 90s.

At full power it is the mixing process of the fast exhaust flow with the surrounding air. Note that noise increases with the sixth to eighth power of jet velocity, so the loudest engines are those with a low bypass ratio  and reheat on.

Diagram from a Stanford web page on noise. The jet velocity is in ft/s.
At idle the biggest noise source of the whole aircraft is the flow around the lowered landing gear, gear cavities and the slotted flaps that you asked us to disregard. The engine noise is a combination of intake noise, bearing noise and nozzle noise, and which of those contributes most to the engine noise depends on the individual engine and its installation into the aircraft.

I am so sorry I never marked this as correct. Have +15

I'm trying to understand your answer, but it's not clear to me. Most of the noise comes from the "mixing process of the fast exhaust flow with the surrounding air". And for a turbofan the diagram shows a 20-35 dB "delta" (the link to the document is dead). I guess 20 dB is not the sound pressure of a turbofan since a hair dryer is already 90 dBA, so what is it and how much loud is this turbofan mixing process?

@mins Bummer that the page is offline. I read it such that the exhaust flow of a turbofan adds another 20 - 36 dB to all other noise sources (gears, intake etc.). What is missing is the distance at which that has been measured! Without the distance the comparison to a hair dryer becomes moot. I intended the graph only as an illustration for the influence the exhaust speed has on noise, not as a reference on absolute noise levels.

dB are logs: 30 dB + to 30dB is not 60 dB, but only 33 dB, and this is still a whisper. If you add 20 dB and obtain the total noise pressure of, say 115 dB for a turbofan, then you need to add this to 115 dB already (115+20=115). So where the 115 did come from in the first place.... dB(A) are usually measured at 3 m and integrated.

@mins You are so right. The person who drew the chart probably added logs like integers. I cannot find the source of the diagram (even with TinEye), so I cannot provide any more background.


text:
How to avoid talking over others when using different send/receive frequencies?
Related to this question about flight services: when I talk to FSS over the generic or the local receive-only frequency while listening to the VOR voice channel, how do I avoid talking over others on the same frequency?
Intuitively, I'd listen to the frequency I'm going to be transmitting on for a bit, then send my request, and then wait for a reply on the other frequency, but that seems like it would be distracting to configure in the radio.
So how would I configure my radio for contacting FSS in this way?
Edit: this is specifically about the case where other aircraft do not necessarily hear the controller speaking to you, so they may start transmitting at any time while I'm receiving the response.

Thats exactly the way you do it for normal 2-way radio communications, only you are listening on the VOR, so why is that distracting?

I'd have to listen to one frequency while waiting to send, and to the other while waiting for a reply, so I have to either switch frequencies (= look at the radio) or listen to both (but 122.2 is going to be busy with talk that doesn't concern me).

Possible duplicate of How do I get attention on a busy radio channel?

I don't think it's a duplicate. This question is about talking on a channel you don't monitor and seems difficult to monitor (the purpose of the question is to know if this transmit only frequency should be monitored). My suggested answer is in that case it's the business of ATC to sort out simultaneous traffic, and in practical this may not be a problem as there could be multiple antennas pointed in different directions on the frequency (so limited RFI) and multiple ATCO behind. Just a guess.

In the specific case of a flight service receive-only frequency you will be able to hear other aircraft transmitting in that frequency (you still listen to your com radio, so treat the transmitting part just like any other transmission and wait for a break before you key the mic).
In the more general case when you have one controller (or Flight Service Specialist) working multiple frequencies you call in when the one you're transmitting on is quiet (and in the case where you're receiving Flight Service over a VOR wait for that to be quiet too).
The controller or FSS will answer you if they're free. If they're busy on another frequency or a landline they'll respond with "Aircraft calling, stand by" (or if they're really busy and don't hear you you won't get a response and you'll try again in a minute).
It's not a perfect system, but it works pretty well most of the time.

So I listen to both COM and NAV, and hope that no one else speaks on the COM frequency while the controller answers my request on the NAV frequency?

@SimonRichter anyone else transmitting on the COM frequency should also be listening on the NAV frequency and so will know not to transmit while the controller is speaking.

Yep, everyone should hear the controller or FSS operator's responses. Other aircraft just may not hear you calling the controller or FSS and you may not hear the other aircraft.

@IanF1 That's not always the case, in fact there's a counterexample right by me: Hampton VOR (HTO) and Groton VOR (GON) both have 122.1 listed as a receive-only frequency. If you're transmitting on 122.1 receiving via HTO someone transmitting on 122.1 and receiving via GON won't hear the replies going to you, and if we go to the extreme ends of the service volume for that RCO you might not hear each other's calls on 122.1 either. (This is admittedly a contrived edge case, but it's still possible: We basically count on the FSS being able to do 2 things at once in this case.)

@voretaq7 thanks for the correction! I assumed they were paired 1 to 1.

@IanF1 They usually are, more or less (adequate distance between RCOs so it's probably not an issue) -- they may even multiplex transmissions so GON & HTO have the same voice channel, I've never had occasion to receive over either VOR so I never checked. I'm not sure there are other situations like this but that one stands out because it's close to home :)

One thing you can do is pay attention to what the controller or FSS says. If you tune in and hear them ask someone a question (i.e. "Cessna 42F, please say type, position, and state request") then it would be wise to give it 30 seconds or so before keying the mic, since they're likely listening to 42F's reply even if you don't hear anything. Otherwise, just make your call and if they don't hear you, usually they'll ask "aircraft calling" to "say again". If you get no response, wait for a break and try again.


text:
What are those aircraft flying over my house?
I took pictures of 6 aircraft at Long Beach, California. Although I see them a lot of times, I have yet to hear the name.
These photos were taken on August 6, 2020:

A blue and orange biplane on 5:34 PM.

A gray, long-winged aircraft on 6:02 PM.
And these photos were taken on August 7, 2020:

A two-bladed rotor blue helicopter on 6:23 PM.

A white, mid-winged aircraft on 7:01 PM.

A white, high-winged aircraft on 7:04 PM.

A black, mid-winged aircraft on 7:19 PM.

One question per post please.

Rather than posting fuzzy pictures here in the hope that someone can identify them, get yourself a reasonable pair of binoculars (10x50 should give good results) and read the registration (the N-number) from under the wing or the fuselage side. You can look those numbers up on the FAA registry. If you find reading those numbers off the aircraft in flight too difficult, head to the airport and do it there. With binoculars and a smartphone you could teach yourself a lot about aircraft recognition in just a couple of hours.

I don't think I am good at asking questions in here; they keep getting downvotes.

@KyleCocjin people have explained to you why these questions got downvoted. it is up to you how to best use this information.

Most likely this question is gonna close after the bounty because of the downvotes.

@KyleCocjin given your questions, I think you should meet some spotters. A quick search points to several pinterest, twitter and facebook accounts.

Isn't this supposed to be closed? It has 4 downvotes.

Two things:

The helicopter is a Robinson R-44.
This is the fourth time you have come on this site to ask the posters to identify aircraft flying out of your local airfield. Do yourself a favor. Go down to your local airfield and become a fixture. You will learn a lot more about the aircraft you are inquiring about from the actual people who fly and maintain them. Most pilots and mechanics are more than happy to share their passion for aviation. Heck! Some of them may even offer you a ride. Then, if you have questions about specific aviation subjects after you have researched them, come to this site and ask. More than likely, you will get the answers from the horses’ mouths at the airfield even before you ask them.

Okay. Someday, I will make another question that may be different. It won’t be aircraft identification on there.

@Kyle Cocjin, I actually laughed out loud after reading Dean's answer then checking your profile!  Good on you for your enthusiasm, but I agree with Dean.  And i think you will get more out of researching aircraft types ahead of time, then trying to ID them yourself rather than just asking others.  But don't be afraid to ask if you get stuck on a tough one, maybe just not every airplane you see...

Okay, I should do this from now on.

+1, mainly for the second paragraph.

1: Boeing Stearman
2: Unknown but possibly part of the Cessna company
3: Robinson R44 or R66
4: Most likely a Cirrus SR-2X
5: Cessna 172RG or 182RG
6: Likely a PA-28 Cherokee

Photo 1: Not totally clear but appears to be a Boeing Stearman
Photo 2: Unknown
Photo 3: Robinson R66 with camera pod, most likely a news or police helicopter.
Photo 4: Unknown. Possibly a Cirrus SR-2X series.
Photo 5: Either a Cessna 172RG or 182RG
Photo 6: Piper PA-28 Cherokee

For future use - there is app that you can run on your phone. Point it at a plane that you see and it will tell you info about the plane. Type w pic, tail number, to, from, speed, height, etc.  It won’t work for every plane, but it works for most. The app is called FlightAware and the function is the AR button. I think the free version has the AR. I think the paid version also displays the FAA registered owner.


text:
What is this jet aircraft appearing in the 2019 TV Series "Black Summer"?
This looks like an F-22 Raptor, but I can hardly see it:

That would be my bet too.

F-22 or F-35. My bet is on F-22.

Air intakes suggest an F22.

Of course you can hardly see it -- the F-22 is stealthy!

If this is in fact an actual plane (or a cgi representation of one, it is most likely a F-22 Raptor.
The picture is very blurry and somewhat distorted (probably due to panning), but features fitting to F-22 are:

Trapezoid twin rudders (F-35 has parallelogram shaped rudders)
Rudders fairly far from each other (twin engine)
Rudders canted outwards (rules out F-15)
Relatively high canopy (i.e. F-35 has the canopy positioned much lower in respect to aft fuselage
Sleek fuselage profile (i.e. F-35 has rather chubby fuselage proportions)
Air intake rather forward (rules out F-18)

Not being familiar with the series this is from, I'm willing to bet this is not an actual plane, but cgi. The 3D -model might be totally fictious, only resembling F-22 in the manner described above.


text:
How are APUs started?
How are jet engines started? says that engines must be started from bleed air, which can come from the APU, another engine, or a huffer cart, or from windmilling.
As far as I understand, APUs are also jet engines. How are they started? In the air, they must be able to start when both engines are out, so are they able to windmill start? On the ground, can they connect to a huffer cart?

I've read that the MD-80 is an example of an airplane that can start its APU via windmilling, though I believe that's not typical.

Considering the APU generates Auxiliary Power, doesn't it typically use its own generator as the starter motor?

@BrianDrummond Some APU do feature generators that double as starter motors when current is applied to them.

747-100/200 aircraft could start the APU in the air but not use it in the air. If started in the air (usually on final approach), electrical power from an engine bus was used. If started when the engines weren't running, battery or ground power was used.

APUs are like small jet engines, small enough to be started electrically. So you would use the power of the battery or an electric ground power cart to spin up the APU by its electric starter motor, and then introduce fuel into it once its spinning fast enough, just like a jet engine is started. Depending on the design, the electric motor will then either act as a generator to supply electrical power back to the aircraft or decouple when a separate generator is used.
The APU will spin up, and besides spinning the electric generator, some pressurized air will be 'stolen' from its compressor to supply "bleed air" for engine starting, the air conditioning packs, etc...
Big APUs like on the Boeing 777 have actually two methods of starting: They have both an air-driven and an electric driven starter motor. The method of operation is as follows: When the APU is started with the engines off, electrical power from battery or ground connection is used. After the flight, the APU will be restarted before the main engines are turned off. In that case, the APU will be started by the air-driven motor rather than the electric motor, with pressurized air supplied by the still-running main engines.
EDIT to answer question in comment:
Depending on size, the APU will take something between 30seconds and 2 minutes to start. The big APU of the 777 will deliver electrical power after 2 minutes or so, small units you are likely to find on regional jets can do that after perhaps 45 seconds. Then, it takes an additional 2-4 minutes until you can extract bleed air from it. That is because taking air from the compressor increases the exhaust gas temperature of the APU, and you want the APU to warm up evenly. The same is true for the shutdown process: You close the bleed-air valve and then let the APU continue to run for another two minutes or so to cool down, then shut it off completely. This lowers the thermal stress on the unit. On modern planes like the 777 this process is automated: You turn the APU selector switch to OFF and that will close the bleed air valve, initiate a 2 minute cooldown period, and eventually turn off the APU completely. The only way to shut it down immediately is in fact the APU FIRE handle.
So, you will turn the APU on typically while you are taxiing in after landing. Because of course you want it to be up and running and ready to take over the air conditioning by the time you are at the gate.
Some APUs like those found on the MD-80s have two settings for bleed air extraction: NORM and ECON. ECON takes less bleed air, thus not increasing the exhaust gas temperature of the APU too much. On particularly hot days, using the APU bleed in ECON might help not overheating the APU if it is to be used for an extended period of time.

Very informative yet simple to understand answer. How long does an APU take to start up? After landing does the process start straight away or can it wait unil you've stopped at the gate?

I have expanded my answer to answer your comment.

@Ben For what it may be worth, at the two 747 carriers I flew for in the 1990s on arriving 747-100 and -200 aircraft, the flight engineer typically started the APUs while the aircraft was still in the air on final approach.

APUs are smaller jet engines that don't have that much rotational inertia that must be developed before they can self-sustain themselves.
So a simple electric starter-motor on battery power that auto disengages once it is running is enough.

I assume the electric starter motor is attached to the accessory drive described in the linked question?


text:
What is "detonation" in a piston engine?
Recently, I saw this question, which included a rather alarming quote:

Full throttle operation with carburetor heat on can cause detonation.

Woah! That doesn't sound good. In fact, I would have figured aviation engine manufacturers would have worked hard to prevent their engines from exploding, and possibly destroying the rest of the aircraft and/or killing the pilot in the process.
I also found this question, with a rather calm quote:

What if I have a noise cancelling headset on, and the engine undergoes detonation?

It seems like there should be other cues that your engine just blew itself to bits...
I'm figuring that perhaps "detonation" in this context doesn't actually mean that your engine block turns into shrapnel. I also figure that it doesn't refer to the normal process of piston engines, where fuel is injected and mixed with fuel before detonating. So what does it mean?

Do you mean http://en.wikipedia.org/wiki/Engine_knocking ?

@orique I think so

detonation does not mean that the engine will explode, means that the mixture of air an fuel will explote by itself without the need of an spark in a typical "gasoline" engine, so working like a "diesel".

@TrebiaProject. That's pre-ignition. Detonation refers to the way the fuel burns, not when it burns. However, detonation and pre-ignition can cause each other. See Nathan's answer. You're right, though, of course, that 'detonation' doesn't mean the engine explodes. The fuel is detonating, not the engine.

@reirab I thought the phenomena was called the same way (basically is the same physical mechanism), thanks for the hint.

@reirab: At least, hopefully not the engine.

Detonation, as the name suggests, is an explosion of the fuel-air mixture inside the cylinder. Under normal operation, the spark plugs each ignite a point in the fuel/air charge, which then propagate through the cylinder and provides a consistent, regulated burn in a process called deflagration. This extends the time that the burning fuel pushes on the cylinder, providing a gentle power stroke.
During detonation, the fuel/air charge (or pockets within the charge) explodes rather than burning smoothly. Because of this explosion, the charge exerts a much higher force on the piston and cylinder, leading to increased noise, vibration, and cylinder head temperatures. The violence of detonation also causes a reduction in power. Mild detonation may increase engine wear, though some engines can operate with mild detonation regularly. However, severe detonation can cause engine failure in minutes. Because of the noise that it makes, detonation is called "engine knock" or "pinging" in cars.

(Source: FAA PHAK, page 6-18)
Detonation can be caused by a number of factors, but generally they relate to a situation outside of the engine's design. Using the wrong fuel can cause detonation: the octane rating of a fuel is basically the amount of pressure it can take before it detonates. Similarly, high cylinder temperatures can cause detonation(1). This is why mixture is set very rich when at high power levels: the excess fuel cools the cylinders, preventing detonation. As noted above, full power with carburetor heat on can cause detonation, as the increased temperature mimics the effect of high cylinder temperatures. Full carburetor heat is required to provide at least a 90 degree F increase in intake air temperature.
Further reading:

Page 6-19 of the Pilot's Handbook of Aeronautical Knowledge.
An article at Savvy Analysis

1) Detonation is distinct from pre-ignition, where the fuel/air charge is ignited by something other than the spark plug. Notably, detonation and pre-ignition often cause each other, as a detonating engine will have a very high CHT (potentially enough to cause pre-ignition), and if the charge pre-ignites as the cylinder is still rising, the continued compression may cause the charge to detonate.

This is implicit in your answer, but to make it explicit since I think it will help OP, the normal mode of burning fuel in an engine is deflagration, not detonation.

So, TL;DR: "detonation", in the present context, doesn't refer to the engine blowing up, but can cause the engine to blow up if it goes on for too long?

I'm sorry, what does it mean "ignite a point in the fuel/air charge" (ignite at the certain point of time or it's something else here?) and also what are pockets here - "During detonation, the fuel/air charge (or pockets within the charge)" Thank you!

Detonation is the instaneous combustion that occur due to unburnt gases left in the combustion chamber resulting in high temperature, sufficient for self-ignition

I'd say, sorry, can't retrieve the reference now, that: 'detonation', is not the same as: 'knocking', even if you consider: 'knocking', as the audible expression of a detonation, or preignition or other forms of undesirable combustion inside an Internal Combustion Piston Engine, be the piston alternative or a rotating rotor.
Toyota tested successfully, 7% fuel economy improvement, a cleaner exhaust, in a Wankel Rotary Engine, substituting a glow-plug in the leading site for the ordinary spark plug. Another concept cited here is the presence of two plugs in aviation engines, my idea was that the purpose of a double plug and double ignition system, e.g. two magnetos, is just a redundancy for safety reasons, having a replacement ignition system in the case of failure of one, but the rate and pace of combustion, or flame front speed inside the working chamber of an ICE is also influenced by having one or more plugs, by the presence of hot spots, swirl or quenching inside the combustion chamber, and by the shape of combustion chamber and valve mechanism, if there's any, but the issue is complex.
The books by Harry Ricardo: 'The high-speed internal combustion engine', a classic of ICEs, deal with this and other combustion issues.                  *link to download the 1931 edition: http://www.mediafire.com/download/gn1o0vyvzaz/The+High+Speed+Internal+Combustion+Engine+Ricardo+1931.pdf
Also available was: 'Aircraft Propulsion', by C. Fayette Taylor, Smithsonian Annals of Flight, 1971.
Hope it's useful for you. Regards. Salut †

Can you explain the difference you see between "detonating" and "knocking"?

I'd say: 'Detonation', is a combustion taking place at a much faster speed than usual, even the whole Fuel/Air mix may ignite instantly, not as a flame front that advances through the mix, and: 'Knocking', may be the noise that a reciprocating piston engine produces when some types of undesirable combustion take place, it could be: 'Detonation', it could be: 'too much mix swirl', or 'too advanced ignition timing' in plug ignited cycles, or a too low Octane fuel, or a 'Hot spot' inside the combustion chamber, or other events that induce pre-ignition, a too early ignition, or self-ignition.

Comment was more a question, requesting somebody's confirmation of previous reading: 'Detonation', &: 'Knocking', not the same, and to explain it more in deep, your question gave me opportunity to explain my previous, perhaps wrong, concepts about this.
Abraham Maslow was right in that everything you learn is put on a basis of the previous knowledge about the subject inside your mind, even when you've heard of that subject first in your life; just hearing a name or about an idea builds concepts, preconcepts or prejudices inside your mind, it's the way we are, or the way our CNS works. Salut +


text:
Which aircraft have elevators (lifts)? How do they work?
This Question came up reading this comment from  tohecz on this question: Is it possible to access the baggage compartment in flight?.

No elevator to the cargo deck like in thriller movies? I'm disappointed :( /sarcasm

According to some statements on Internet, there are elevators(lifts) on 747s for persons and carts.

Does anybody have any evidence or photos of their existence on smaller planes than A380s?
How do they work?
Do they have an electric-motor department on top (This will take much space)?
Where are they going to? Are they going to the personnel sleeping cabin? (On the A380 it makes sense)

This one from a A380 doesn't seem for persons?

Oh, those sorts of elevators. The first half of this question had me very confused.

they probably use rack and pinion gears to move the cage, much lighter though not as powerful than the counterweight system

@jamiec thanks, I edited it. You were right, question was irritating if you have the tail elevator in mind.
Also thanks to ratchet freak for "rack and pinion gears".

The last picture looks like it is for transporting galley carts.

I recall that some DC-10s had galley elevators as well from my reading of a DC-10 FCOM.

After researching myself and asking a colleauge I found out that the L-1011(one of my favorites)

and the DC-10 (thanks to @UnrecognizedFallingObject for the comment)

had persons elevator.
On the Tristar and the DC-10
The purpose are to connect the Main Deck with the personnel-cabin or the Lounge.
.
The Mechanism as "@ratchet freak" stated in the comment is an "rack and pinion gears" elevator with 1 electric motor with 1 outer shaft (primary) and 1 inner shaft, as stated in an report of an incident with one of these elevators.
On the A380 there is an elevator to connect the 2 main decks, but this one is only for trolleys.

Edit:
Additional Information on mechanism of elevator:

Drive System
Each lift is operated by an independent drive unit. Each drive 400-cycle, three-phase,
  alternating current (AC) motors. Each motor is connected to a gearbox with
  counter-rotating drive shafts and sprockets for a chain drive. The drive shafts are
  operated by a common worm gear within the gearbox. In the
  event of one motor failure, the other motor will drive the lift at
  half-speed. Two, independent, continuous loop, bicycle-type chains taking power from the
  dual-output sprockets on the drive units actively drive each lift.

Limit Switches
The range of travel of the lifts is controlled by limit switches installed
  within the wire duct attached to the forward side of one of the vertical lift
  tracks. There are two sets of two limit switches for each lift:
  one set located in the service center and one set in the lower galley.
  One switch is a normal stop switch and the other limit switch is for
  overtravel in the event the normal switch fails to operate.
  The limit switches are actuated by a cam plate mounted on the side of the lift.
  The cam plate has a machined offset to prevent actuation of the
  overtravel limit switch unless the normal switch fails to operate. In
  addition to the limit switches, mechanical stops are installed in the
  vertical lift tracks to stall and shut off the gear motors if both
  limit switches malfunction.

Further and detailed Information can be found here in this Incident.

In my opinion the 2 linked Incidents also show that they are not really safe, probably that's why on the A380 they only made a Trolley-Lift.

and they were never meant for people, I seriously doubt any sane person would use them to transport people except in dire emergencies.

I worked as a mechanic on 747's for Pan Am and several other airlines and never seen a people elevator in any of the 747's I worked on.
Ironically today ( Oct. 21, 2020) I was looking at accident/incident reports on the NTSB's website and ran across a report of an accident where a flight attendant was seriously injured in an elevator accident on a 747 in 1988.
https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001213X27351&AKey=1&RType=Summary&IType=LA
Freak accident due to poor design. She entered not realizing the elevator was not on her floor. Just then another flight attendant entered the elevator from the upper deck and proceeded downward when she heard the screams of the flight attendant below her and stopped the elevator before it crushed the flight attendant . The attendant below suffered spinal fractures and cuts.

Your submission is more like a comment than an answer, but I'm curious about why you never saw a lift on planes that are known to have them.

While I agree with @ErinAnne, it does, in a round-about way, answer the question by stating that 747s have elevators, since there was an incident involving people in the elevator. Could do with a strong [edit] to highlight the answer portion.


text:
How does the squat switch work?
This question came up after reading the following comments on the answer to this question: Raising the flaps right after touchdown. Good or bad?
Philippe Leybaert Jan 20 at 23:00

The retractable landing gear is an excellent point. It makes perfect
  sense. I've read a few stories of pilots retracting the gear after
  landing instead of raising the flaps.

voretaq7♦ Jan 20 at 23:02

The retractable landing gear issue is particularly notable because
  early in the landing roll you may not have enough weight on the wheels
  to activate the squat switch that prevents you from retracting your
  gear while you're using them to hold the plane up. Your perfect
  landing could turn into a nice, smooth gear-up incident if you bump
  the wrong switch.

Questions

How does the squat switch work (which prevent gear up on the ground)?
Are there any reports on issues of gear up on ground? (I only know
one)?

A more formal name is "weight-on-wheel switch". It can actually be anything from a strain gauge on the landing gear leg to a contact switch which is activated by the oleo strut position.

@PeterKämpf: Another name sometimes seen is "ground-shift mechanism".

The squat switch is essentially a sensor that senses if the weight of the aircraft is resting on the gear. This can be done by load cell or displacement sensor on the suspension arm.
Like any other component these sensors can fail though engineers prefer them to fail in an always on (weight on the gear) state; that way the pilot just needs to deal with gear failing to retract after takeoff and needing to land again to check it out rather than dropping the plane on the ground and causing more damage.

As one visual example, here's the squat switch from a King Air. When the plane is resting on the gear the strut is compressed, and the scissor link is bent as you see it here. When weight comes off the wheels the strut extends and the metal piece attached to the fork presses the switch, signaling the rest of the system that there is no weight on that wheel.


text:
What are these paint patches on this 787-8?
What are these paint patches on this British Airways 787-8 (G-ZBJB)?

They are fixed spots where the surface paint has peeled off. Both Boeing and Airbus have been having this issue with their newer models.
Manufacturers are stressing that this is simply a cosmetic nuissance:
https://mentourpilot.com/is-boeing-also-dealing-with-peeling-paint-issues/

One of the major causes of that kind of pain adhesion is mechanics touching the structure with silicone grease residues on their hands.  Extremely difficult to remove.

"Pain adhesion"; sounds about right ;)

As an airline (paying customer) I would also got mad about this. A cosmetic nuisance is if the color becomes matte of timer, not peeling off.

Agreed 100% Ratrod look don't suit airliners...

Sounds like Boeing and Airbus have decided to switch paint suppliers to whomever GM has been using for the last couple of decades.


text:
Are turbine and compressor blades and vanes cast or forged?
I was wondering how blades and vanes are typically made in commercial jet engines. Would you typically use investment casting to make compressor blades or just in the turbine section to accommodate the cooling channels?
Also, how much does a first stage high pressure turbine blade cost? Are they more expensive on the newer engines, for example, the LEAP vs. CFM56?

I found this video.It may provide partial answer.

Gas turbine blades are super-high-tech castings... https://www.americanscientist.org/article/each-blade-a-single-crystal

Thanks! Looks like the turbine blades are largely casted, and based on the video, the compressor blades seem to be forged - could you make a compressor blade with investment casting? Just trying to understand why some are forged and others are cast

@xxavier Please post that as an answer.

@Bianfable The OP's question refers not only to the manufacture of turbine blades, but also to compressor blades and to turbine blade absolute and relative costs... The American Scientist article that I quoted covers casting methods for turbine blades only...

As a summary,
The fan blade is made by shaping molten titanium in a hot press. When removed, each blade skin is welded to a mate, and the hollow cavity in the center is filled with a titanium honeycomb.
The compressor blades are made by casting
Turbine blades are made by forming wax copies of the blades and then immersing the copies in a ceramic slurry bath. After each copy is heated to harden the ceramic and melt the wax, molten metal is poured into the hollow left by the melted wax
Please refer to the following website, it is very interesting for the manufacturing process of the main engine parts:
http://www.madehow.com/Volume-1/Jet-Engine.html
Concerning the fan blades:

Each fan blade consists of two blade skins produced by shaping molten titanium in a hot press. When removed, each blade skin is welded to a mate, with a hollow cavity in the center. To increase the strength of the final product, this cavity is filled with a titanium honeycomb.

Concerning the compressor blades:

Casting is used to form the compressor blades. In this process, the alloy from which the blades will be formed is poured into a ceramic mold, heated in a furnace, and cooled. When the mold is broken off, the blades are machined to their final shape

Concerning the turbine blades, it is multi-process:

Turbine blades, however, are made by a somewhat different method than that used to form compressor blades, because they are subjected to even greater stress due to the intense heat of the combustor that lies just in front of them. First, copies of the blades are formed by pouring wax into metal molds. Once each wax shape has set, it is removed from the mold and immersed in a ceramic slurry bath, forming a ceramic coating about .25-inch (.63-centimeter) thick. Each cluster is then heated to harden the ceramic and melt the wax. Molten metal is now poured into the hollow left by the melted wax. The internal air cooling passages within each blade are also formed during this stage of production.
The metal grains in the blade are now aligned parallel to the blade by a process called directional solidifying. The grain direction is important because the turbine blades are subjected to so much stress; if the grains are aligned correctly, the blade is much less likely to fracture. The solidifying process takes place in computer-controlled ovens in which the blades are carefully heated according to precise specifications. The metal grains assume the correct configuration as they cool following their removal from the oven.
The next and final stages in preparing turbine blades are machine-shaping and either laser drilling or spark erosion. First, the blade is honed to the final, desired shape through a machining process. Next, parallel lines of tiny holes are formed in each blade as a supplement to the interior cooling passageways. The holes are formed by either a small laser beam or by spark erosion, in which carefully controlled sparks are permitted to eat holes in the blade.

The cost of old models parts could be very expensive because they are manufactured upon request, that was the case for Concorde engines.
The financial aspect of the question is beyond my scope

At least some blades are 'grown' from a single seed crystal, within the confines of a mould, so that the finished product is itself a single crystal of metal.


text:
How does the regulatory body CAA link to aviation?
How does the regulatory body CAA link to aviation?

Welcome to aviation.SE. I'm sorry, but I am not really sure how to answer you here. What do you know about the CAA? where have you looked and what exactly is unclear to you? the function that the CAA has? what do you mean with "link to aviation"?

There's a wikipedia page on the UK CAA here: https://en.wikipedia.org/wiki/Civil_Aviation_Authority_(United_Kingdom). Furthermore the CAA's page itself is pretty clear on what it does.

Brief answer:
The CAA ensures that all flying in the country, be it small planes, or major airlines, are acting in accordance with policies, standards and aviation law. These standards and laws are written by ICAO (International Civil Aviation Organisation), and presuming you are referring to the UK CAA, standards and policies can also come from EASA (European Union Aviation Safety Agency) [at the time of writing]. Any differences in the standards, policies and laws from ICAO are listed in the CAA's AIP
These standards, policies and laws which the CAA are responsible for regulating cover a wide range of areas: pilot's licenses to meteorological equipment and standards, rules of flying in the air (e.g. distance from cloud, filing flight plans) to aviation medicals, charts and NOTAMs  to compensation claims, drone safety at airports to aircraft design and parts, airport lights and signs to air traffic services available... [the list goes on...]
Basically, anything related to flying, the CAA will govern according with international rules written by ICAO (and EASA).


text:
What year did the seat belt sign come in to use?
What year did commercial airlines start using a lighted seat belt sign?

Based on my research, seatbelt signs must've been introduced before or during the DC-3 era, however, I couldn't go into further depth to give you a definitive answer. Hope this helps though.

related: When-did-airlines-start-using-seat-belts-for-passengers

The earliest reference to seat belt signs I can find is Scheduled Air Carrier Rules, 14 C.F.R. (1941)

§ 61.342 Seat belt sign. An aircraft shall not be operated in
scheduled air transportation unless a suitable means for warning
passengers to fasten seat belts is provided. [As added by Amdt. 129,
CAR, Sept. 5, 1941, effective Oct. 1, 1941, and Amdt. 130, CAR, Sept.
12, 1941; 6 P.R. 4691, 4753]

https://www.loc.gov/item/cfr1943001-T14CIP61/
The amendment appears in 6 FR 4753
https://www.loc.gov/item/fr006181/
It's unclear where the motivation for this regulation came from, but it is likely mentioned in the Civil Aeronautics Board's meeting minutes for September 5, 1941. Unfortunately it does not appear that these minutes have been digitized. The relevant records should be available in the National Archives RG 197.2.


text:
What materials form the structural elements of the Boeing 737?
What materials form the structural elements (leaving the spars, ribs etc) of the B737?
It was tough to get any information on the kind of composites used on the 737 structure. Hoping to get some information on that.

This question is too vague. I’m not sure what parts you want to know about. I remember reading about Boeing using graphite-epoxy composites for the stabilizers, I think. Maybe be more specific about individual parts.

I'm working on a college project, which requires me to find material alternatives for the 737. So, I wanted to know what the original components were so that I can search of materials according to their characteristics or even better.

Most of the Boeing 737's structure is made in aluminium. Composites are used for smaller parts like the ailerons, the wing-to-body fairings and the tail cone.
It looks like all of the control surfaces are composites.

Medium capacity airliner series. Aluminium alloy wing structure, upper skin and tail plane, with graphite composite elevator, rudder and ailerons. Glass or carbon fibre-reinforced plastic nosecone, fairings and fin tip. Single or split-scimitar double winglets.

more composite components:
The nosecone, wing and fuselage fairings, fin tips, the fairings of the flap actuators and other non-stressed components are constructed from glass and carbon fibre reinforced plastics (GFRP and CFRP). The rear of the engine nacelles are constructed of graphite, Kevlar and glass fibre composites.
In February 2000 an advanced carbon graphite winglet developed by Boeing became available as an option on the 737-800.


text:
What is the angle $\epsilon_{cl}$ in this diagram?
Here is an image showing the geometric significance of $\epsilon_{cl}$. To me it looks like the angle between the tangent of the underside of the trailing edge and horizontal (V infinity).

Here is a formula for $\epsilon_{cl}$:
$$ \epsilon_{cl} = \frac{1.62 C_{L_w}}{\pi A} $$
$C_{L_w}$ is the coefficient of lift of the wing and $A$ is the aspect ratio.

What is the source of the image (unless you created it)?

Estimation of aircraft aerodynamic center for
conventional, canard, or three-surface aircraft v0.9
Based on Dr. Jan Roskam’s Aircraft Design Series

its from this document, I don't know if you can find it online. Its about the multhopp method.

This is the downwash angle. Consider it an angle by which the wing deflects the airflow behind it.
Traditionally, this angle is designated $\epsilon$. Why the $cl$ index I don't know; perhaps it reinforces its direct dependency on the wing lift coefficient, as you can see from the formula; or that this is the 'pure' downwash only dependent on the wing. In fact, every document should have a Nomenclature section which explains the designations.
Apart from $C_L$ and $A$, the effective downwash angle will depend on the distance from the wing and spanwise location. Typically, the point of interest is the tailplane: downwash reduces its effective angle of attack. The coefficient $1.62$ probably accounts for the tail location ($z_h$ etc.), but you need to double check how this $\epsilon$ is used. (You will find different coefficients in the literature).
Obviously, this will affect trimming. But downwash also has a significant effect on stability, because it changes dynamically with lift. As the angle of attack / lift (of the wing) increases, downwash also increases. Therefore, the horizontal tail experiences a reduced variation of angles of attack compared to the wing. This is further complicated by the fact that this reduction is delayed by the time it takes for the airflow to reach the tail. Generally, these are positive effects, but they must be accounted for in stability analysis.

The cl stands for the centerline. The equation shows that this is the downwash angle and the factor 1.62 is normally 2 when wing and tail are in one plane. Here the T-tail reduces this factor to 1.62, as you say. +1.


text:
What is the difference between an Airbus A330-200 and an A330-243?
I am just curious to know the difference between Airbus A330-200 and A330-243.
Sri Lankan Airline A330-243

Sri Lankan Airline A330-200

Airbus has a dash numbering system that specified the engine manufacturer and the engine variant in addition to the aircraft's series number. The system details can be found here:
http://www.aerospaceweb.org/question/planes/q0276a.shtml

The general format of the Airbus numbering system is Ammm-sevZ where the individual components are described below.

Ammm = model number
s = series number
e = number defining the engine manufacturer
v = number defining the version of the engine model
Z =  optional letter describing a variation of the series number

The series number refers to the different variants of a particular model that have been developed. Standard series numbers used by Airbus include 1 for 100, 2 for 200, etc. The primary exception to this system is the A300. The original series number designations used for variants of this model included the B1, B2, and B4 for passenger models as well as the C4 for a convertible freighter version. Later production variants of the A300 were designated as the A300-600 to become consistent with the rest of the Airbus product line.
The engine manufacturer codes that have been assigned to date include the following.

0 = General Electric (GE)
1 = SNECMA
2 = Pratt & Whitney (PW)
3 = International Aero Engines (IAE)
4 = Rolls-Royce (RR)
5 = Engine Alliance (joint venture of GE and PW)

The final number denotes newer
versions of the basic engine model. These numbers appear to start at 1
for the original engine and increase sequentially for updated engines.
An optional letter sometimes follows the series of numbers to
designate a variation on the series number. Common examples include
the following.

C = convertible passenger/freighter model
F = freighter model
R = long range model
X = enhanced model (?)

thats helps, thanks :)

The engine manufacturer and type numbers are specific to the model. For A320 (A318–A321) they are different: 1 is CFM56, 2 is PW6000, 3 is IAE2500, 5 is CFM LEAP and 7 is PW1000G.


text:
Which dust size causes most damage to turbine engines?
I'm conducting some research on my bachelor's thesis on predictive maintenance and I have so far not been able to find a solution to the following question:
Which size of dust is more damaging to the engine when it comes to ingested dust?
So far I have found some papers covering the topic or moderately related to it but I can't seem to find a precise answer directly relating particle size and damage (i.e. from 200µm to 500 µm the damage is severe but under 200 µm much smaller damage is presented; for particles bigger than 1 mm no damage is presented as they do not enter the turbines)
I hope someone has found some insight on this topic.
Thank you very much.

Are you specifically asking about damage to the turbine blades? My naïve understanding would be that the fan or compressor blades would be damaged more by dust, but maybe I'm wrong...

Any damage is relevant. I just figured out that it would be easier to relate particle size with turbine damage, but i might be mistaken.

OK, I phrased the title a bit more generic now. Feel free to edit again if you need something more specific.

I wouldn't be surprised if the type of dust has a much larger influence than the size. Volcanic ash is detrimental because of its low melting point, sand can be highly abrasive, but I can't imagine sawdust having any effect regardless of size.

Yes the type of dust makes a difference . Sodium Sulfate is not hard but can melt and cause "hot corrosion" on some of the lower alloy blades. Also there is variety of exotic blade coating materials used to protect them ; I believe from both oxidation and erosion. ,

Thank you very much for your reply, @Sanchises.
I will take that into consideration.

I appreciate your answer @blacksmith37. Do you know of any other heavily damaging aerosol to keep an eye on? Or where could one find such information?


text:
What would happen if a hot air ballooon was punctured in mid-air?
I am writing a script for a film where a hot air balloon is punctured and it falls to the ground. There are two teenagers in the balloon when it is in the air. What I would like to know is how fast the balloon would fall the ground. Would it glide down or would it drop? This might be a dumb question but it would really help me out in the story. If it helps at all, the balloon is supposed to crash land on top of a canopy tree. Would the balloon go down like an airplane and crash landed, nosediving towards the earth at a fast speed or would the rest of the balloon slows its velocity down?
I need the characters to survive the crash and the tear will be about 4 inches. Would it need to be longer for the balloon to start descending for a crash landing?

I think the answer is that it depends completely on the size of the hole...  pin prick, hardly noticeable.  Massive rip? It could drop like a stone.  Do you want the characters to survive?

@MichaelHall I want the characters to survive and the hole is about 4 inches in length.

@DigitalDracula Thanks! That really helps!

What causes the hole?  Do you need to specify the actual size?

@Katherine, as DeanF says a 4 in hole isn't going to matter much, a 4 foot rip would make things interesting though. But don't worry about making it realistic, it needs to fit the expectation of the audience. 4 feet is enough to look realistic without seeming silly, and gives plenty of opportunity for peril.

The fabric is rip-stop - there are strong threads running through the fabric which stops rips from spreading to far. However, I don't know how far apart the threads are

Hot-air Balloons are already made with large holes in them. They are called vents. They can be located in the balloon’s top or sides. They tend to be much much larger than the 4-inch diameter you described in your question. But, their opening and closing are controlled by the pilots. Research the FAA Balloon Flying Handbook. It will give you much more insight than I can.

you can fly with large holes, the fabric is a rip stop nylon so long as the fabric is in good shape (you have 100 hour/annual inspections (in usa) like any other aircraft) the rip wont stop.
A large hole maybe a few feet long, and depending on where on the envelope you find this hole, it may require you to burn more often than you would normally, to compensate but it is not a case of falling to the ground at some computed rate.
Likewise the age of the fabric is more porous.  so the same balloon new vs its last year of life before failing will involve burning more often or longer with the older balloon.
holes in balloons are the fiction of movies and tv shows.
Now if you during pre-flight see even a small hole then technically you are not to take off without a repair or whatever.  But if you end up in the air or brush a tree, etc, then you deal with it.
One of my balloons I had to be careful with where the crown line was placed, if it was placed next to one of the turning vents it would keep the vent open which you dont find out about until you are in the air and the balloon starts to spin faster and faster.  fortunately I had vents in both directions so it was a matter of extra or longer burns plus pulling the other vent to stop the spin every so often.   lots of heat being lost, but was able to find a landing spot and learn the lesson for that brand/model to watch where the crown line was placed.


text:
Why can't lifting line model be applied to yawed/skewed/oblique straight wing (low M)
If all the horseshoe vortices have skewed central bound vortices on the same skewed 1/4 chord line, then the trailing vortices from the downwind half span  of the wing induce less on the windward halfspan and vice versa. So then the windward halfspan of the wing will have increased angle of attack and lift vs unskewed and the leeward have less.
But I gather this is the wrong result vs experiment? Please don't confuse the issue with symmetrical swept back wings. No, I  used Lifting Line to generate results that disagree with experiments for asymmetrical oblique or yawed straight wings? What am I overlooking ?

Lifting Line analysis is not suitable for low aspect ratio wing, highly swept wing or a wing undergoing large sideslip, because each of these would have significant spanwise flow gradient.
To see why, it's worth revisiting the central equation of the Lifting Line, applicable to a planar wing:
$$c_l(y)=a_0 \left[ \alpha - \frac{w(y)}{V_\infty} - \alpha_{L=0} + \theta_t(y) \right]= \frac{2}{V^2_\infty c(y)} \lVert \vec{V}_\infty \times \vec{\Gamma}(y) \rVert$$
where $y$ is the spanwise coordinate of the section, $c_l$ is the 2D airfoil lift coefficient, $a_0$ is the 2D airfoil lift slope, $\alpha$ is the free-stream angle of attack against the wing, $w$ is the downwash generated by the trailing vortices1, $\alpha_{L=0}$ is the 2D airfoil zero-lift angle of attack (or aerodynamic twist), $\theta_t$ is the geometric twist of the section, $c$ is the section chord length, $\vec{V}_\infty$ and $V_\infty$ are the vector and magnitude of the free-stream air velocity against the wing, and $\vec{\Gamma}$ is the bound vortex strength at the section2.
The left hand side of the central equation is the 2D airfoil lift and the right hand side is the lift we expect from the circulation generated by the bound vortex. Assuming the 2D characteristics are known in advance (i.e. the 2D lift slope, zero lift AOA, etc), and the wing geometry is known (chord length at every section), then we should be able to calculate the unknown, $\Gamma$, at every section.
To put it crudely, Lifting Line is cheating: it relies on you knowing the 2D airfoil characteristics apriori, in order to calculate the 3D lift and drag (which is its biggest advantage). The downside is that it inherently assumes the 2D data tells the whole story; all influences from the neighbouring sections are lumped into a single downwash (induced AOA), which remains 2D. In a highly swept or sideslip'ed wing, this assumption breaks down.

1 $w$ can be calculated using Biot-Savart from the trailing vortices (which have constant strength, $d{\Gamma}/dy$, along the filament), but will need to be slightly modified from the typical result shown for the Classical Lifting Line (which is only applicable for straight tapered wing), since the trailing legs are parallel to the freestream, not the bound vortex.
2 Note that I've used the vectorized version of the Kutta-Joukowski Theorem since in a swept or sideslip'ed wing the bound vortex and freestream aren't perpendicular.